I have a database which contains a lot of data and although I was not involved in setting it up it is what I have to work with.
Within this database is somewhat of a lookup table. However, this table has no link to any other tables. It essentially takes the following form
ID | input | table_name |
-------------------------------------
1 | Movie | movie_tbl |
2 | Cartoon | cartoon_tbl |
3 | Animation | cartoon_tbl |
4 | Audio | audio_tbl |
5 | Picture | picture_tbl |
The table is a lot larger than the above, but the structure is as above. So what happens is someone visits my site. Here, they have an input field. Say they enter Movie then the above table is called to find the input with Movie. It then gets what table it needs to look in. I would imagine that the query would be something like
SELECT table_name FROM lookup_table WHERE input LIKE Movie;
Now that should return movie_tbl. I now know that I need to search for Movie within movie_tbl and return all the data for its row. So movie_tbl might be like this (data would be some type of data and the column names different)
ID | input | col_1 | col_2 | col_3 |
----------------------------------------------------
1 | Movie | data | data | data |
2 | Cartoon | data | data | data |
3 | Animation | data | data | data |
4 | Audio | data | data | data |
5 | Picture | data | data | data |
So now my query will be something like this
SELECT * FROM movie_tbl WHERE input LIKE Movie;
Now the tables have tens of thousands of lines of data. My real question is whether the above will be effecient or not? With the database I was given however, I do not see any other way I could do this (I cant touch the database). Is there anything I can do to make this more effecient?
Any advice appreciated
Thanks
Why are you checking for input in the 2nd table? You have already filtered the input from the first table:
SELECT table_name FROM lookup_table WHERE input LIKE Movie;
In this case you dont have to make 2 queries. Just the 2nd one should suffice. Or just having Movie data in the 2nd table and separate tables for Cartoon, Animation etc. Because then you wont be accessing the 'WHERE' clause, just:
SELECT * FROM movie_tbl;
2nd Suggestion: Use = instead of LIKE. No need for pattern matching if you know the exact input string.
Related
I have a MySQL table that looks like this (attached below).
I want to simultaneously select (in a single SQL Query) multiple columns (id, Last Name, and username) and import into them into different lists of strings the values if they meet a certain condition (in this case, where color="blue".
+----+------------+-----------+----------+----------------+
| id | First Name | Last Name | Username | Favorite Color |
+----+------------+-----------+----------+----------------+
| 1 | John | Smith | jsmith | Blue |
| 2 | Avery | Nelson | aNelson | Red |
| 3 | Jack | Brooklyn | jBrook | Blue |
| 4 | Arnold | Nam | aNam | Blue |
| 5 | Charlie | Smith | cSmith | Orange |
+----+------------+-----------+----------+----------------+
... Continued
I am trying to select all the required data that meet the condition where color=Blue with the MySQL query of SELECT id, Last Name, username FROM `myTable` WHERE color="Blue". Once this data is selected, I want to import each selected column that meets the color requirement into separate lists.
For example, list FirstName should be list of strings "John, Jack, Arnold" (in that order) and Username list should contain "jsmith, jBrook, aNam" etc. In the end, I want to be able to produce three lists that contain these values which meet the Favorite Color condition in the MySQL database of Blue. How can I do this?
I know that I can make three separate reader queries but I want to do them all in one to save time.
You have not posted VB code so I'm not sure how you intend to use the results but you could load the whole table to a Datatable (unless it is really big), then use Dataview.RowFilter to filter your data with different criteria in-memory, without making any further request to the database backend.
You can see an example in VB.net here
Then you could use LINQ for example to generate a list of string from a datatable or view, see here for an example.
In short; we are trying to return certain results from one table based on second level criteria of another table.
I have a number of source data tables,
So:
Table DataA:
data_id | columns | stuff....
-----------------------------
1 | here | etc.
2 | here | poop
3 | here | etc.
Table DataB:
data_id | columnz | various....
-----------------------------
1 | there | you
2 | there | get
3 | there | the
4 | there | idea.
Table DataC:
data_id | column_s | others....
-----------------------------
1 | where | you
2 | where | get
3 | where | the
4 | where | idea.
Table DataD: etc. There are more and more will be added ongoing
And a relational table of visits, where there are "visits" to some of these other data rows in these other tables above.
Each of the above tables holds very different sets of data.
The way this is currently structured is like this:
Visits Table:
visit_id | reference | ref_id | visit_data | columns | notes
-------------------------------------------------------------
1 | DataC | 2 | some data | etc. | so this is a reference
| | | | | to a visit to row id
| | | | | 2 on table DataC
2 | DataC | 3 | some data | etc. | ...
3 | DataB | 4 | more data | etc. | so this is a reference
| | | | | to a visit to row id
| | | | | 4 on table DataB
4 | DataA | 1 | more data | etc. | etc. etc.
5 | DataA | 2 | more data | etc. | you get the idea
Now we currently list the visits by various user given criteria, such as visit date.
however the user can also choose which tables (ie data types) they want to view, so a user has to tick a box to show they want data from DataA table, and DataC table but not DataB, for example.
The SQL we currently have works like this; the column list in the IN conditional is dynamically generated from user choices:
SELECT visit_id,columns, visit_data, notes
FROM visits
WHERE visit_date < :maxDate AND visits.reference IN ('DataA','DataC')
The Issue:
Now, we need to go a step beyond this and list the visits by a sub-criteria of one of the "Data" tables,
So for example, DataA table has a reference to something else, so now the client wants to list all visits to numerous reference types, and IF the type is DataA then to only count the visits if the data in that table fits a value.
For example:
List all visits to DataB and all visits to DataA where DataA.stuff = poop
The way we currently work this is a secondary SQL on the results of the first visit listing, exampled above. This works but is always returning the full table of DataA when we only want to return a subset of DataA but we can't be exclusive about it outside of DataA.
We can't use LEFT JOIN because that doesn't trim the results as needed, we can't use exclusionary joins (RIGHT / INNER) because that then removes anything from DataC or any other table,
We can't find a way to add queries to the WHERE because again, that would loose any data from any other table that is not DataA.
What we kind of need is a JOIN within an IF/CASE clause.
Pseudo SQL:
SELECT visit_id,columns, visit_data, notes
FROM visits
IF(visits.reference = 'DataA')
INNER JOIN DataA ON visits.ref_id = DataA.id AND DataA.stuff = 'poop'
ENDIF
WHERE visit_date < 2020-12-06 AND visits.reference IN ('DataA','DataC')
All criteria in the WHERE clause are set by the user, none are static (This includes the DataA.stuff criteria too).
So with the above example the output would be:
visit_id | reference | ref_id | visit_data | columns | notes
-------------------------------------------------------------
1 | DataC | 2 | some data | etc. |
2 | DataC | 3 | some data | etc. |
5 | DataA | 1 | more data | etc. |
We can't use Union because the different Data tables contain lots of different details.
Questions:
There may be a very straightforward answer to this but I can't see it,
How can we approach trying to achieve this sort of partial exclusivity?
I suspect that our overarching architecture structure here could be improved (the system complexity has grown organically over a number of years). If so, what could be a better way of building this?
What we kind of need is a JOIN within an IF/CASE clause.
Well, you should know that's not possible in SQL.
Think of this analogy to function calls in a conventional programming language. You're essentially asking for something like:
What we need is a function call that calls a different function depending on the value you pass as a parameter.
As if you could do this:
call $somefunction(argument);
And which $somefunction you call would be determined by the function called, depending on the value of argument. This doesn't make any sense in any programming language.
It is similar in SQL — the tables and columns are fixed at the time the query is parsed. Rows of data are not read until the query is executed. Therefore one can't change the tables depending on the rows executed.
The simplest answer would be that you must run more than one query:
SELECT visit_id,columns, visit_data, notes
FROM visits
INNER JOIN DataA ON visits.ref_id = DataA.id AND DataA.stuff = 'poop'
WHERE visit_date < 2020-12-06 AND visits.reference = 'DataA';
SELECT visit_id,columns, visit_data, notes
FROM visits
WHERE visit_date < 2020-12-06 AND visits.reference = 'DataC';
Not every task must be done in one SQL query. If it's too complex or difficult to combine two tasks into one query, then leave them separate and write code in the client application to combine the results.
I have a database in mysql which has three rows, these rows has concatenated multiples values(values separated by a comma) already in it. I want to strike the rank using find_in_set function or any better function to get the positions.
Table
id | NUMBERS |
1 | 30,40,10 |
2 | 58,29,21 |
3 | 18,25,51 |
I want to rank each row in this format
id | NUMBERS | POSITION |
1 | 30,40,10 | 2,1,3 |
2 | 58,29,21 | 1,2,3 |
3 | 18,25,51 | 3,2,1 |
I Know the data representation and structure is wrong, but the data i have currently is made like the above and has a lot of data in it, meaning changing the structure would take me a lot of time, although I would change it later.
I need a workaround idea as to how to do this. I would be grateful for your support thanks.
I've got multiple entries in table A and would like to display the number of entries in a coloumn of table B. Is there a way to create a dynamic cell-content displaying the number of entries in a table?
I'm a beginner in MySQL and did not find a way to do it so far.
Example table A:
+----+------+------------+
| id | name | birthday |
+----+------+------------+
| 1 | john | 1976-11-18 |
| 2 | bill | 1983-12-21 |
| 3 | abby | 1991-03-11 |
| 4 | lynn | 1969-08-02 |
| 5 | jake | 1989-07-29 |
+----+------+------------+
What I'd like in table B:
+----+------+----------+
| id | name | numusers |
| 1 | tblA | 5 |
+----+------+----------+
In my actual database there is no incrementing ID so just taking the last value would not work - if this would've been a solution.
If MySQL can't handle this the option would be to create some kind of cronjob on my server reading the number of rows and writing them into that cell. I know how to do this - just checking if there's another way.
I'm not looking for a command to run on the mysql-console. What I'm trying to figure out is if there's some option which dynamically changes the cell's value to what I've described above.
You can create a view that will give you this information. The SQL for this view is inspired by an answer to a similar question:
CREATE VIEW table_counts AS
SELECT table_name, table_rows
FROM information_schema.tables
WHERE table_schema = '{your_db}';
The view will have the cells you speak of. As you can see, it is just a filter on an already existing table, so you might consider that this table information_schema.tables is the answer to your question.
You can do that directly with COUNT() for example SELECT COUNT(*) FROM TblA The you get all rows from that table. If you IDXs are ok then its very fast. If you write it to another table you have to make an request too to get the result of the second table. So i think your can do it directly.
If you have some performance problems there are some other possibilities like Triggers or Stored Procedures to calculate that result and save them in a memory table to get a better performance.
I need help with a Query, i have a table like this:
| ID | codehwos |
| --- | ----------- |
| 1 | 16,17,15,26 |
| 2 | 15,32,12,23 |
| 3 | 53,15,21,26 |
I need an outpout like this:
| codehwos | number_of_this_code |
| -------- | ---------------------- |
| 15 | 3 |
| 17 | 1 |
| 26 | 2 |
I want to sum all the time a code is used in a row.
Can anyone make a query for doing it for all the code in one time?
Thanks
You have a very poor data format. You should not store lists in strings and never store lists of numbers in strings. SQL has a great data structure for storing lists. Hint: it is called a "table" not a "string".
That said, sometimes one is stuck with other people's really poor design choices. We wouldn't make them ourselves, but we still need to get something done. Assuming you have a list of codes, you can do what you want with:
select c.code, count(*)
from codes c join
table t
on find_in_set(c.code, t.codehwos) > 0
group by c.code;
If you have any influence over the data structure, then advocate for a junction table, the right way to store this data in a relational database.